The present invention relates to a tool head, in particular for dentistry instruments or handpieces, and to the method of embodying such a head.
In the art field of dental surgery, use is made in particular of turbine handpieces comprising a grip of which one end carries a head serving to support and retain a bur, the actual tool which is inserted by the surgeon into the oral cavity of the patient. The rear end of the handpiece is connected to fluid lines carrying pressurized air and water, which are directed along the length of the grip and emerge at the head; the air serves to rotate the turbine, and in addition, a mixture of air and water is sprayed from a set of holes converging on the tip of the bur, cooling the cutting edges and the treatment area and functioning also as a cleansing agent. The head itself is of circular section, and affords a housing at the side remote from the bur in which the turbine or rotor is stably accommodated, whilst the bur side incorporates a small annular seating designed to hold a coaxially disposed metal insert, likewise annular, retained in a fluid-tight fit; this same insert (e.g. as disclosed in EP 236 820) constitutes a working part of the head from which the spray of cooling fluid is released, and to that end is embodied with outlet holes and connected to internal passages carrying the air and the water through the handpiece.
In assembly, the insert and the head are united by a force fit in conjunction with sealing means, an arrangement which is a source of problems regarding the structural architecture of the head as a whole; in effect, the addition of the insert increases the axial dimension of the head, a factor occasioning practical difficulties when maneuvering in the oral cavity around the dental treatment area.
In another type of embodiment (see EP 109 507), the preference is for a capacious seating on the side of the bur which allows the introduction, from the top, of a generously proportioned insert similarly affording ducts for the passage of the fluids and associated with seals for assembly of the head as a whole. Here too, the same drawbacks are encountered as described above, and in addition the insert has to be fashioned separately from the head through to the final configuration, with all the attendant consequences deriving from the need for precision fits between corresponding diameters (down to some few tenths of one millimeter).
What is more, in both the embodiments mentioned, the part of the spray circuit encompassed by the insert-and-head assembly is relatively consistent in volume, and water can therefore stagnate in the head during the pauses when the handpiece is not in use. Again, in these conventional embodiments, the passages afforded by the insert are positioned in a variety of circumferential arrangements designed to obtain a spray converging on the tip of the bur, and while this ensures that the treatment area and the tip are kept clean, it does not always favor or afford good lateral vision to the operator of the handpiece.
Moreover, the insert will not always be positioned faultlessly following assembly, and in particular, a lack of coaxial alignment between corresponding air and water passages can result in the correct operating conditions being impaired.
Accordingly, the object of the present invention is to overcome the aforementioned drawbacks through the adoption of a head for dentistry handpieces in which the geometry of the internal air and water passages is such as to ensure a safe and hygienic spray, affording optimum vision for the operator of the handpiece, and in which a more practical and superior level of design is achieved.